This disclosure relates generally to drive systems for aircraft control surfaces, and more particularly to hydraulic drive systems for moving and controlling the aircraft control surfaces.
All aircraft include movable control surfaces for directional control in flight. Such control surfaces can include ailerons for roll control, elevators for pitch control, and rudders for yaw control. In addition, most conventional jet transport aircraft typically include leading edge slats and trailing edge flaps on the wings. These devices can be used to generate high lift during takeoff and landing when the aircraft is traveling at relatively low air speeds.
Federal aviation regulations (FARS) impose airworthiness standards on lift and drag devices for transport category aircraft. For example, FAR xc2xa725.697 requires that such devices (e.g., trailing edge flaps) must maintain selected positions (e.g., extended positions) without further attention by the pilot. This requirement applies at all times during flight. Thus, lift and drag devices must be able to maintain extended positions even in the unlikely event of a general failure of the aircraft""s power system.
Trailing edge flaps (xe2x80x9cflapsxe2x80x9d) on jet transport aircraft typically deploy aft of the wing and downward to increase wing area and camber. The flaps are typically powered by a drive system having a drive shaft that extends longitudinally inside the wing and is coupled to a central power drive unit. The drive shaft for each wing is connected by a system of gears to a series of ball screws and linear actuators distributed along the length of the wing adjacent to the flaps. Rotation of the drive shaft in a first direction causes the ball screws to rotate in a corresponding direction, thereby extending the flaps on the wing. Similarly, counter rotation of the drive shaft causes the ball screws to counter-rotate, thereby retracting the flaps. Flap drive systems are mechanically interconnected to provide wing-to-wing symmetry of the trailing edge flaps on both wings. Such wing-to-wing symmetry, or equivalent, is required by the current FARs. These conventional drive systems, however, can be very heavy and costly.
Hydraulic drive systems with linear actuators have also been used for flap drive systems. For safety purposes, these hydraulic flap drive systems are typically designed to include built-in backup or redundant systems. Accordingly, the hydraulic flap drive systems are powered by two hydraulic systems and utilize twice as many linear actuators as are required to handle the system loads. The resulting hydraulic flap drive systems tend to weigh more and cost more than the drive systems using the drive shafts and gears.
Aspects of embodiments of the invention are directed to drive systems for aircraft control surfaces, such as trailing edge flaps and leading edge slats. One embodiment provides an actuator control system for controlling first and second control portions. The system comprises first and second supply lines and a return line coupleable to a source of fluid. A fluid-driven actuator is connected to at least one of the first and second control portions. The fluid-driven actuator is in fluid communication with the first and second supply lines. A flow control assembly is connected to the first supply line and to the return line. The flow control is configured to control the flow of fluid in one direction from the first supply line to the fluid-driven actuators and to control the flow of fluid in another direction from the fluid-driven actuator to the return line. A bypass line is in fluid communication with the first and second supply lines and is positioned to provide fluid from the second supply line into the first supply line at a position intermediate the source and the fluid-driven actuator.
Another embodiment provides an aircraft system having first and second control surfaces, a source of hydraulic fluid, a first control system coupled to the first control surface, and a second control system coupled to the second control surface. Each of the first and second control systems comprises first and second supply lines coupled to the source of hydraulic fluid, and a return line coupled to the source of hydraulic fluid. A hydraulic actuator is connected to at least one of the first and second aircraft control surfaces. The hydraulic actuator is movable between first and second positions, and is configured to receive hydraulic fluid from the first supply line when the hydraulic actuator moves toward the first position. The hydraulic actuator is also configured to receive hydraulic fluid from the second supply line when the hydraulic actuator moves toward the second position.
A flow-blocking member is coupled to the first and second supply lines and is movable between an open position and a closed position. The flow-blocking member, when in the closed position, prevents movement of the hydraulic fluid to and from the hydraulic actuator. A flow control assembly is connected to the return line and to at least one of the first and second supply lines. A bypass line is in fluid communication with the first and second supply lines. The bypass line is positioned to direct hydraulic fluid from one of the first and second supply lines into the other one of the first and second supply lines upstream of the hydraulic actuator. The bypass line recycles the hydraulic fluid back into the other one of the first and second supply lines when the hydraulic actuator moves toward the first position. A computer controller operatively interconnects the first and second control systems.
Another aspect of the invention includes a method of making a control surface drive system. The method can include connecting first and second supply lines and a return line to a source of fluid, and connecting a plurality of fluid-driven actuator assemblies to the first and second supply lines and to the return line. The method can also include connecting the fluid-driven actuator assemblies to at least one control surface and connecting a flow control assembly to the return line and to at least one of the first and second supply lines. The method can also include connecting a bypass line to the first and second supply lines in a position to direct fluid from one of the first and second supply lines into the other one of the first and second supply lines at a position intermediate the source of fluid and at least one of the fluid-driven actuators when the at least one of the fluid-driven actuators moves toward the first position to recycle the fluid back into the other one of the first and second supply lines.